This invention relates to a method of attaching a bottom plate made of a plastic material to one end of an open-ended, hollow cylinder made of a plastic material and an apparatus suitable for carrying such method into practice.
In one method known in the art of attaching a bottom plate made of a plastic material to one end of an open-ended, hollow cylinder made of a plastic material to obtain a plastic cylindrical container, (see FIGS. 1a and 1b) a bonding agent 2 is applied to a fitting portion of a bottom plate 3 to be fitted to an outer wall surface or an inner wall surface of a cylinder 1 and the cylinder 1 and the bottom plate 3 are bonded together to thereby obtain the plastic cylindrical container. In another method (see FIG. 1c), the cylinder 1 is fitted in a peripheral groove formed in the bottom plate 3 to receive the cylinder 1 and a seal is provided by using high frequency techniques in which high frequency electrodes plates 4 and 4' are pressed against the cylinder 1 and the bottom plate 3. Some disadvantages are associated with these known methods. In the method using a bonding agent, the bonding agent used which have deleterious effects may migrate to the contents of the cylindrical container, the bonding agent used may be so low in bond strength that the containers produced may not be suitable for practical use, and the bond provided may vary from container to container, thereby reducing productivity. Moreover, the use of a bonding agent requires a bonding agent applying step in the method. Meanwhile the method of using high frequency techniques disclosed in Japanese Patent Gazette No. 13118/66 which is shown in FIG. 1c requires a complex mechanism for providing a high frequency welding and raises the problem of maintenance. Also, the strength of the seal provided by high frequency techniques varies from one container to another, and it has hitherto been impossible to obtain stability in the quality of the products.
Further, in another prior art of Japanese Patent Publication No. 29146/79, since a bottom plate receiving portion formed at the end of a plastic hollow cylinder is prepared mainly by using the shrinkage property of the plastic cylinder caused by the heating thereof, there had been occurred such defects that the configuration of the end of a resultant cylinder vessel varys, the quality thereof being not stable and the productivity thereof being reduced.